Hand-washing cloth masks only increases the risk of COVID-19 contamination but machine-washing them can make them as safe as surgical masks, according to new research.
Professor Raina MacIntyre, of UNSW Sydney's Kirby Institute, says cloth and surgical masks should be considered contaminated after use.
While surgical masks are single use, cloth masks are re-used and need to be washed daily at high temperatures to protect against infection.
Doing so means "a machine-washed cloth mask is as effective as a surgical mask," she says.
"While it can be tempting to use the same mask for multiple days in a row, or to give it a quick hand-wash or wipe-over, our research suggests that this increases the risk of contamination," she said in a statement after her team's research was published this week in the peer-reviewed BMJ Open online journal.
The researchers analysed unpublished data from a randomised controlled trial they published in 2015, which they say is still the only such trial ever conducted on the efficacy of cloth masks in preventing viral infections.
Using that data on Vietnamese workers in high-risk hospital wards using cloth masks, the researchers found if the masks were washed in the hospital laundry they were as effective as a surgical mask.
"Healthcare workers who self-washed their masks by hand had double the risk of infection compared to those who used the hospital laundry," Prof MacIntyre said.
"The World Health Organisation recommends machine washing masks with hot water at 60 degrees Celsius and laundry detergent, and the results of our analysis support this recommendation.
"Washing machines often have a default temperature of 40C or 60C, so do check the setting. At these very hot temperatures, handwashing is not possible."
From Monday Victorians have been warned they must wear a fitted face mask outdoors - scarves and bandanas will be unacceptable - or risk a police fine.